Developer Reference for Intel® oneAPI Math Kernel Library for Fortran
A newer version of this document is available. Customers should click here to go to the newest version.
?lagv2
Computes the Generalized Schur factorization of a real 2-by-2 matrix pencil (A,B) where B is upper triangular.
call slagv2( a, lda, b, ldb, alphar, alphai, beta, csl, snl, csr, snr )
call dlagv2( a, lda, b, ldb, alphar, alphai, beta, csl, snl, csr, snr )
- mkl.fi
 
The routine computes the Generalized Schur factorization of a real 2-by-2 matrix pencil (A,B) where B is upper triangular. The routine computes orthogonal (rotation) matrices given by csl, snl and csr, snr such that:
1) if the pencil (A,B) has two real eigenvalues (include 0/0 or 1/0 types), then
 
   
 
   2) if the pencil (A,B) has a pair of complex conjugate eigenvalues, then
 
   
 
   where b11≥b22>0.
- a, b
 -  
     
REAL for slagv2
DOUBLE PRECISION for dlagv2
Arrays:
a(lda,2) contains the 2-by-2 matrix A;
b(ldb,2) contains the upper triangular 2-by-2 matrix B.
 - lda
 -  
     
INTEGER. The leading dimension of the array a;
lda≥ 2.
 - ldb
 -  
     
INTEGER. The leading dimension of the array b;
ldb≥ 2.
 
- a
 -  
     
On exit, a is overwritten by the "A-part" of the generalized Schur form.
 - b
 -  
     
On exit, b is overwritten by the "B-part" of the generalized Schur form.
 - alphar, alphai, beta
 -  
     
REAL for slagv2
DOUBLE PRECISION for dlagv2.
Arrays, dimension (2) each.
(alphar(k) + i*alphai(k))/beta(k) are the eigenvalues of the pencil (A,B), k=1,2 and i = sqrt(-1).
Note that beta(k) may be zero.
 - csl, snl
 -  
     
REAL for slagv2
DOUBLE PRECISION for dlagv2
The cosine and sine of the left rotation matrix, respectively.
 - csr, snr
 -  
     
REAL for slagv2
DOUBLE PRECISION for dlagv2
The cosine and sine of the right rotation matrix, respectively.